Information drives business. Companies today rely to an unprecedented extent on online, frequently accessed, constantly changing data to run their businesses. Unplanned events that inhibit the availability of this data can seriously damage business operations. Additionally, any permanent data loss, from natural disaster or any other source, will likely have serious negative consequences for the continued viability of a business. Therefore, when disaster strikes, companies must be prepared to eliminate or minimize data loss, and recover quickly with useable data.
Companies have come to rely upon high-availability clusters to provide the most critical services and to store their most critical data. In general, there are different types of clusters, such as, for example, compute clusters, storage clusters, scalable clusters, and the like. High-availability clusters (also known as HA Clusters or Failover Clusters) are computer clusters that are implemented primarily for the purpose of providing high availability of services which the cluster provides. They operate by having redundant computers or nodes which are then used to provide service when system components fail.
Normally, if a server with a particular application crashes, the application will be unavailable until someone fixes the crashed server. HA clustering remedies this situation by detecting hardware/software faults, and immediately restarting the application on another system without requiring administrative intervention, a process known as Failover. As part of this process, clustering software may configure the node before starting the application on it. For example, appropriate file systems may need to be imported and mounted, network hardware may have to be configured, and some supporting applications may need to be running as well.
HA clusters are often used for critical databases, file sharing on a network, business applications, and customer services such as internet commerce websites. HA cluster implementations attempt to build redundancy into a cluster to eliminate single points of failure, including multiple network connections and data storage which is multiply connected via storage area networks or Internet protocol based storage.
Companies must minimize data loss and implement DR (disaster recovery) quickly in case disaster strikes. For example, a flood, hurricane, earthquake, or the like, can disrupt services and infrastructure across wide areas. Replication technology is primarily used for data distribution and DR. Periodic replication is one technique utilized to minimize data loss and improve the availability of data in which a point-in-time copy of data is replicated and stored at one or more remote sites or nodes. In the event of a site migration, failure of one or more physical disks storing data, or failure of a node or host data processing system associated with such a disk, the remote replicated data copy may be utilized.
Multi-tier applications representing a business service are often required to be managed as a single unit for HA/DR (high availability/disaster recovery). Generally, a multi-tier architecture refers to a client-server architecture in which the presentation, the application processing, and the data management are logically separate processes. For example, an application that uses middleware to service data requests between a user and a database employs a multi-tier architecture.
Multi-tier applications representing a business service need to be managed as a single unit for HA/DR. For example, various applications and processes that embody the functionality of the business service need to brought online or offline, switched over, failover or failed back as a single unit within or across different cluster sites.